C6-0 make a C6-P

I put tandem motors on the MIT test stand and had the curves.
There was a very short and not that violent blip when the booster motor
burned through and then a slight dip as the booster propellant was completely consumed and the upper stage was just coming up to thrust.
The perfect example of the burn through spike that Bob is trying to describe is the AVI Gold Series motors. Let's look at two examples that used a looong 18mm casing and a looong 24 mm casing. They were basically booster motors and then they had a seperate smaller casing containing a delay train and ejection charge that was epoxied into the top. When first produced, the motors were extremely long and the 18mm was a full 20 Ns and the 24 mm was a full 40 Ns (unless I'm remembering wrong and they were just short of "full"). Anyway, when they burned, the casings got really thin from erosion. Not as bad as if they had been tandems, but still extremely thin. Some burned through the sidewall, but MANY blew through the sidewall as the propellant burned out. The forward face of the propellant would ignite as soon as the flame front blew through and since the aft face was already burning, it had a momentary spike of at least double the thrust. Since it was not open on top, the pressure equalized almost instantly on both sides of the rupture, so you did not get giant chunks of propellant breaking off and sending the peak thrust/pressure explosively high. However, the peak was enough to blow out the casing at it's thinnest.
Solution: they de-rated the motors, cutting about 5 Ns off each one and making the casings shorter. They also painted inhibitor on most of the forward face of the propellant before epoxying in the delay/ejection housing.
Estes had to do some casing magic to get the E9 motor to work with the long burn time, but they did not have to worry about the burnout spike, since they have integral delays.
-Fred Shecter NAR 20117
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Bob Kaplow wrote:

Hey Bob, Chad said that he did that with his boost glider and it never failed for him. If it works every time for him and he is not lying then I don't know how he could be refuted.
Kurt Savegnago

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True, I've never had a failure. Now, I haven't flown 100 motors like this, but have done multiple. Will it eventually fail....yes, everything will. The key is packing the wadding as tight as possible AND several layers of tape.
I'm probably gonna jinx myself by posting this. I can see it now, some contest has C RG and I do this and completely toast my radio gear. :) Just because I opened my mouth and said it has worked. Always watch out for Murphy...
chad
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CouldBeFlying wrote:

I did the opposite one time. Took an E9-P and made it an EP-0 to put into a Quest Zenith II. Had a ceramic plug and used a twist drill by hand to remove the plug by going down to the black powder. Launched and successfully recovered. Sim said 2700-2800 feet with a C6-7 sustainer. Note Well! I did this on my time at an isolated field, by myself and NOT at an organized launch. Was a cool flight but will not do it again as the risk of losing such a small model is so great.
I suspect you could achieve the same thing with some sort of heat resistant plug and a high temperature adhesive. Durham's water putty might make a satisfactory plug material follow by a glob of J & B weld. One has to remember the guy is going to use a C6-0 with no ejection charge. One only has to worry about burn through. My removal by hand of the plug in the E9-P was dirt easy and the plug actually didn't seem to be that strong.
Kurt Savegnago
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wrote:

WWHD?
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